1. Field of the Invention
This invention relates to machining techniques for use with polycrystalline diamond.
2. Description of the Related Art
It is known, for example in the manufacture of cutters for earth boring drill bits, to form a relatively large diameter polycrystalline diamond component bonded to a substrate, and then to machine the component to cut the component into a plurality of pieces. This technique for use in the manufacture of cutters is described in, for example, U.S. Pat. No. 6,011,232 and EP 0857537.
The machining technique used in the manufacture of such a cutter is most often an electron discharge machine (EDM) technique, and relies upon the component being machined being of electrically conductive form. Generally, polycrystalline diamond components comprise a plurality of diamond crystals defining therebetween a matrix of interstices. The interstices usually contain a catalyzing material, typically cobalt, used in the formation of the polycrystalline diamond and in bonding the diamond to the substrate. The presence of cobalt in the interstices renders the component electrically conductive and hence suitable for use with electron discharge machining techniques.
It has been found that the abrasion resistance of a polycrystalline diamond cutter can be increased by removing the catalyzing material from a volume of the polycrystalline diamond close to a working surface thereof. Although treatment of the polycrystalline diamond to render the interstices close to the working surface substantially free of catalyzing material improves the wear resistance, it also results in the part of the polycrystalline diamond close to the working surface being of poor electrical conductivity and hence electron discharge machining techniques cannot be used effectively in machining polycrystalline diamonds so treated.
It is an object of the invention to provide a technique whereby machining of such polycrystalline diamonds can be achieved in a simple and convenient manner.
According to the present invention there is provided a machining method comprising treating a polycrystalline diamond component of the type including a volume close to a working surface that is substantially free of catalyzing material to render the polycrystalline diamond electrically conductive, and using an electron discharge machining technique to machine the polycrystalline diamond material.
The polycrystalline diamond may be plated with an electrically conductive material to render it conductive. Alternatively, an infiltration technique may be used to infiltrate a conductive material into the interstices from which catalyzing material has been removed to render the polycrystalline diamond electrically conductive.
Where a plating technique is used, the polycrystalline diamond may be plated with a layer of nickel or another metallic material.
Where an infiltration technique is used, the technique may involve vacuum impregnation of a conductive paint, a graphite suspension or another electrically conductive material into the interstices. Alternatively a pressure impregnation technique may be used with, for example, graphite or other electrically conductive media such as a mounting compound.